Things that bother me in ours, our bath had a basic shower head attached to a diverter on the taps, that was fine. But the bath's angled ends made showering a bit of a pain. So if you do a combined bath shower, just think about your footing. P shaped baths in my mind are ugly. But practical. Perhaps just stick to separate bath and shower.
I don't much enjoy it when partner comes in and craps while I am in the bath. So a separate toilet outside the bathroom would suit.
Copper taps, far more hygienic, kills e-coli.
I like to be able to get my head under a basin tap. To rinse mouth etc. Many tap/sink setups don't work for me.
As our toilet is not on external wall, I think we could have hid the soil pipe under the floor.
Hot and cold tap in one, would really help me wash in the basin. But I'm not sure if this is a problem? Should you have a separate cold tap for oral use only? Thinking about bugs that can thrive in hot water systems pipes.
I like to have a shower that I can move to parts I want to wash. Two heads: one fixed and one hose would be nice.
I must admit, being able to shower the toilet for cleaning is quite useful.